1. Field of the Invention
This invention relates to improved chromatographic devices and methods of preparing them. The improved chromatographic devices of the invention are useful in analytical chromatography, particularly in immunochromatography.
A number of materials are known for use as chromatographic media. Generally, the material is "bibulous" or "porous," such as that found in a random or oriented pile of fibers of cellulose, fiberglass, etc., in powdered silica, and the like. Chromatographic material is generally used in a chromatographic device, wherein the material is traversed by a component of a mixture. The component is generally in equilibrium with a mobile phase, usually a liquid medium, most usually a solvent.
Devices in which chromatographic material is employed take many forms. For example, the device may be a strip cut from a sheet of bibulous material, e.g., paper. On the other hand, the device may be a support on which a chromatographic material is contained. Exemplary of the latter is a chromatographic plate which contains, e.g., silica or the like.
Chromatographic strips are normally prepared from larger sheets from which they are cut by mechanical means. The most widely used form of mechanical cutting involves at least one blade or wire.
Mechanical cutting of the sheet into strips results in a deformation of the edge of the strip along the cutting line. This deformation takes the form of a compression of the edges of the strip by the blade or wire. In fibrous strips the fibers which form the strip are pushed closer together at the edges when compared to the distance between the fibers in the body of the strip. This deformation of the edges of the strip frequently results in a faster rate of traversal for the mobile phase at the edges of the strip than through the body of the strip. The front of the mobile phase and other components traversing the strip becomes concave rather than flat.
In many situations in which a chromatographic device is employed, it is important that the shape of the front formed by a component of a mixture traversing the chromatographic material be controlled. In analytical chromatography it is usually preferable to have a flat or convex front whereas in preparative chromatography a flat front is required. An example of such a situation is affinity chromatography in which antibodies are attached to a porous insoluble support. During migration of an antigen-containing solution on the porous support, migration of the antigen solute is specifically delayed in comparison to the migration of the solvent and other solutes. The relative delay decreases with increasing antigen concentration. Accurate quantitation of the concentration of analyte in a sample to be analyzed requires that the position of the analyte front relative to the solvent front be measured accurately. The position of a flat or convex front can usually be measured with greater precision and accuracy than that of a concave front, and a higher degree of accuracy could thereby be obtained in a chromatographic assay. Moreover, in preparative chromtography a linear front permits more ready separation and isolation of the pure conponent.
2. Brief Description of the Prior Art
U.S. Pat. No. 4,168,146 describes an immunoassay employing immunochromatography with antigens followed by contacting the immunochromatograph with an aqueous solution containing labelled antibodies. An enzyme chromtographic immunoassay is described in U.S. Ser. No. 398,505, filed July 15, 1982, now U.S. Pat. No. 4,434,504.